The present invention relates to a system by which cargo transport vehicles, such as straddle carriers for transporting containers and like large cargoes, can be prevented from turning sideways, i.e. turning over and lying on one side.
The straddle carrier itself has a large height and carries a large-sized container or like heavy cargo as held at an elevated level and is therefore subjected to a great centrifugal force when turning. Since the straddle carrier is used at a wide work site, it is required that the carrier run at a speed, for example, of several tens of kilometers per hour which is relatively high for working vehicles of this type. The centrifugal force acting on a running vehicle is proportional to the second power of its speed, so that the straddle carrier frequently turns over on one side when turning at a high speed.
When considering the fact that the centrifugal force acting on a turning vehicle is in proportion to the square of speed and in inverse proportion to the turning radius, it appears useful to control the turning radius of the vehicle running at a high speed so that the turning radius will increase in proportion to the second power of the speed. This can be realized, for example, by limiting the output angle of the power steering system when a high speed is reached, or by giving an increased reaction to the steering wheel at a high speed to necessitate a greater force for turning the handle. However, if the output angle of the power steering system is made variable with the speed, the turning radius of the vehicle varies with the speed even when the angle of rotation of the steering wheel is definite, giving a strange feel to the driver, hence being hazardous. Further if the steering wheel is given an increased reaction, a great force is needed also for returning the steering wheel to its neutral position. What is most important, the centrifugal force relates also to the height and weight of the cargo on the vehicle, so that it is impossible to completely prevent the vehicle from turning sideways merely by controlling the vehicle in accordance with the speed alone.